Wednesday, September 2, 2015

What are the Minimum Minimums for Digital Typical Controllers?

Minimum minimums are the
minimum airflow limits Titus recommends for accurate airflow control on
terminal unit inlets. Many customers have noticed that Titus’ 2014-15 Product
Catalog contains updates regarding these values. In this entry, we will reference
the “DESV - Digital Typical Controller” section found on pg. M14.

The original minimums that
we established many years ago were based on factory-calibrated pneumatic
controls. It was determined that factory-calibrated controls could maintain an
accuracy of +5% if we did not try to set the minimum airflow limit
too low. Of course, you can always order a unit set for full close-off because
that is not really airflow control.

For the Titus II and IIA,
we determined that a minimum airflow based on a sensor signal of 0.03 in wg
could be controlled within +5%. The Titus I required a slightly
higher sensor signal of 0.05 in wg in order to deliver the same accuracy.
Later, analog and digital electronic controls were assumed to be equivalent to
the Titus II and IIA controls with regard to the minimum control accuracy.

During the preparation of our latest catalog, it was decided these minimum
values should be reduced in recognition of the improvements that have occurred
in digital electronic controls (specifically, their electronic flow sensors).

We reduced the minimums
based on a sensor signal of 0.01 in wg. As always, the actual flow-control
accuracy depends on the quality of the controller, but our lab testing has
shown that some controllers can provide +5% accuracy down to a
sensor signal of 0.005 in wg.

Here are the latest
minimums for digital controls:

Size 04 = 30 cfm

Size 05 = 40 cfm

Size 06 = 45 cfm

Size 07 = 70 cfm

Size 08 = 90 cfm

Size 09 = 120 cfm

Size 10 = 145 cfm

Size 12 = 190 cfm

Size 14 = 300 cfm

Size 16 = 385 cfm

Size 40 = 720 cfm

Titus’ minimum minimums for
digital controls are much lower than they have ever been. This should be a
welcome change for designers whom want accurate airflow control without
increasing the minimum airflow volume to achieve it. We have redefined how low
you can go!